The introduction of fuel into the cylinders of an internal combustion engine is most commonly achieved using fuel injectors. A commonly used injector is a closed-nozzle injector which includes a nozzle assembly having a spring-biased needle valve element positioned adjacent the injector nozzle for allowing fuel to be injected into the cylinder of an internal combustion engine. The needle valve element also functions to provide a deliberate, abrupt end to fuel injection. The needle valve is positioned in the injector body and although biased downward by a spring force, a hydraulic force acting on the needle valve primarily holds the needle valve in the closed position. When an actuated force exceeds the biasing hydraulic force or causes a change in the magnitude of the hydraulic force, the needle valve element moves to allow fuel to pass through the injector nozzle, thus marking the beginning of the fuel injection event.
Internal combustion engine designers have increasingly come to realize that substantially improved fuel supply systems are required in order to meet the ever increasing governmental and regulatory requirements of emissions abatement and increased fuel economy. As such one aspect of fuel supply systems that has been the focus of designers is the need to produce alternative fuel injector designs that utilize fewer component parts and therefore contribute to reduced manufacturing costs. If such goals are to be attained fuel injector designs must evolve to yield reliable high quality fuel injectors that perform effectively but which are also less expensive to produce.
For instance, manufacturers have implemented extra high pressure injection systems, also known as XPI, where the pressures can reach 2600 bar. Such high injection pressures create smaller fuel droplets and higher injection velocity to promote more complete burning of the fuel, which increases power and fuel economy. In addition, pollution is reduced because the high thermal efficiencies result in low emissions of hydrocarbons (HC) and carbon monoxide (CO). By injecting required amounts of fuel in a shorter time frame, a high pressure system can accommodate multiple injection events during each combustion cycle. As a result, the engine control software can tailor combustion for particular conditions.
The use of very high injection pressures, however, requires conventional fuel injectors to operate with correspondingly high force levels. In general, to move the needle valve into an open position and cause the injection of fuel, solenoids and their corresponding stator assemblies must act against a preload force that seals the high pressure fuel in the fuel injector. For instance, in one type of fuel injector design, an injector body with a lower chamber filled with high pressure fuel is employed to bias the needle valve in the closed position, and the solenoid opens a plunger valve in the upper chamber in order to expose the lower chamber to a low pressure drain. When the fuel drains from the lower chamber, the pressure in the lower chamber drops and is no longer able to keep the needle valve in the closed position. In order to open the plunger valve, the solenoid must act against the preload force that seals high pressure in the lower chamber. Thus, all internal components in such fuel injectors must work together to provide large forces due to the high pressure which exists in the fuel injector.
Additionally, as injection pressures increase, greater forces must be applied to the injector components of the injector body to achieve the required sealing at the component interfaces/joints. Moreover, injectors often include internal component configurations which are well suited to achieving desired high pressure performance characteristics but do so at high design and manufacturing costs. Consequently, there is a need for a lower cost common rail fuel injector having an improved pilot valve inlet and outlet orifice arrangement and a unique armature and plunger guide arrangement.